+namespace llvm {
+
+// The po_iterator_storage template provides access to the set of already
+// visited nodes during the po_iterator's depth-first traversal.
+//
+// The default implementation simply contains a set of visited nodes, while
+// the Extended=true version uses a reference to an external set.
+//
+// It is possible to prune the depth-first traversal in several ways:
+//
+// - When providing an external set that already contains some graph nodes,
+// those nodes won't be visited again. This is useful for restarting a
+// post-order traversal on a graph with nodes that aren't dominated by a
+// single node.
+//
+// - By providing a custom SetType class, unwanted graph nodes can be excluded
+// by having the insert() function return false. This could for example
+// confine a CFG traversal to blocks in a specific loop.
+//
+// - Finally, by specializing the po_iterator_storage template itself, graph
+// edges can be pruned by returning false in the insertEdge() function. This
+// could be used to remove loop back-edges from the CFG seen by po_iterator.
+//
+// A specialized po_iterator_storage class can observe both the pre-order and
+// the post-order. The insertEdge() function is called in a pre-order, while
+// the finishPostorder() function is called just before the po_iterator moves
+// on to the next node.
+
+/// Default po_iterator_storage implementation with an internal set object.
+template<class SetType, bool External>
+class po_iterator_storage {
+ SetType Visited;
+public:
+ // Return true if edge destination should be visited.
+ template<typename NodeType>
+ bool insertEdge(NodeType *From, NodeType *To) {
+ return Visited.insert(To);
+ }
+
+ // Called after all children of BB have been visited.
+ template<typename NodeType>
+ void finishPostorder(NodeType *BB) {}
+};
+
+/// Specialization of po_iterator_storage that references an external set.
+template<class SetType>
+class po_iterator_storage<SetType, true> {
+ SetType &Visited;
+public:
+ po_iterator_storage(SetType &VSet) : Visited(VSet) {}
+ po_iterator_storage(const po_iterator_storage &S) : Visited(S.Visited) {}
+
+ // Return true if edge destination should be visited, called with From = 0 for
+ // the root node.
+ // Graph edges can be pruned by specializing this function.
+ template<class NodeType>
+ bool insertEdge(NodeType *From, NodeType *To) { return Visited.insert(To); }
+
+ // Called after all children of BB have been visited.
+ template<class NodeType>
+ void finishPostorder(NodeType *BB) {}
+};
+
+template<class GraphT,
+ class SetType = llvm::SmallPtrSet<typename GraphTraits<GraphT>::NodeType*, 8>,
+ bool ExtStorage = false,
+ class GT = GraphTraits<GraphT> >
+class po_iterator : public std::iterator<std::forward_iterator_tag,
+ typename GT::NodeType, ptrdiff_t>,
+ public po_iterator_storage<SetType, ExtStorage> {
+ typedef std::iterator<std::forward_iterator_tag,
+ typename GT::NodeType, ptrdiff_t> super;